A NAND type flash memory device having a three-dimensional structure has been known as a kind of semiconductor device. In manufacturing the NAND type flash memory device having a three-dimensional structure, a step of etching a multilayered film configured by alternately laminating a silicon oxide film and a silicon nitride film is performed so as to form a deep hole in the multilayered film. Such an etching is disclosed in U.S. Patent Application Publication No. 2013/0059450.
Specifically, U.S. Patent Publication No. 2013/0059450 discloses a method for etching a multilayered film by exposing an object to be processed (“workpiece”) having a mask on a multilayered film to plasma of a processing gas.
By the way, a workpiece, which is an object to be etched, may include a first region including a multilayered film configured by alternately laminating a silicon oxide film and a silicon nitride film and a second region including a silicon oxide film having a film thickness larger than that of the silicon oxide film of the first region. It is requested that a space such as, for example, a hole be simultaneously formed in both of the first region and the second region by etching the workpiece. In such etching, a mask is formed on the first region and the second region, and the first region and the second region are etched in a portion exposed form an opening of the mask.